When you try to close a pouch, a fairly substantial air bubble is fatally left in the spout, no matter how close you try to level the liquid to the edge of the spout. This is due to the diameter of the spout and the fact that a liquid tends to form an arc at the surface of a spout.

I think the solution is to have a very thin and long spout (see my post #28) on a squeezable bottle, so that when you squeeze the bottle before capping it, whatever air is left in there, say a 1 millimeter long bubble, it will still be a cylinder 1mm tall and 2 mm wide, which is a really tiny bubble.

To empty the bottle out, one would uncap it, let air in through the spout, remove the cap and quickly pour it out.

I'm not sure I'd be so quick to discard the idea. My main interest is just to store chemicals from one evening's printing session to the next opportunity, which might be a few days or a week later.

OK, a thin neck will reduce the amount of oxidation, but for my purposes any bottle that's full to the neck will be fine. The worst is having a bottle that's full only to the shoulder. Glass marbles are irritating as you observed, and they have to be cleaned. I thought your pouch idea was a great way to avoid all this.

Anyway, there's a free 1 litre sample pouch on its way to me, so I'll let you know how good it is.

I really don't see the need to over-complicate this issue.... if all one want is to have developer stock solution last as long as the manufacturer says. It can be done with commonly available "Data Bottles".

In my past experience with D-76, Dektol and XTOL, using commonly available DATA BOTTLE type plastic containers allowed me to keep the working solution for rated duration, at least. The trick is to minimize introduction and repeated introduction of fresh oxygen to the mix. When I used one 1 gallon bottle for D-76 and Dektol, last few "servings" of solutions were considerably dark and weak. Having bottle opened so many times and fresh oxygen getting in dozens of time must have done it in. I think I threw some away back then.

What I do now is this:
Freshly mixed stock solution gets decanted to a series of bottles.
ONE 1/2 gallon data bottle
ONE 1/4 gallon data bottle
ONE or TWO 1/8 gallon data bottle (used for XTOL which comes in 5 liter bag)
Remainder goes to up to FIVE 8 oz bottles of similar materials.

Start using from smaller bottles. Note, each smallest bottle is "one serving" per bottle. Once all small bottles are empty, larger one get decanted into small bottles. This process continues until the largest one get decanted to remaining smaller ones.

This way, re-introduction of oxygen is limited and number of bottles required are minimum. In my experience, they last at least 8 months. I also have an added convenience of one bottle being per serving.

It works for me.

By the way, there are no Data Bottles in 8 oz sizes. I use plastic bottles that are made of the same material as Data Bottles. Picking wrong type of plastic resulted in early degradation so it is important to watch for the right plastic code at bottom.